Milling inserts are removable tips with multiple cutting edges used in milling applications. They can be rotated (indexed) so that when one of the cutting edges wears down, another cutting edge can be used without affecting the overall quality of the insert. Rather than replacing an entire tool after its cutting edges are worn, only the inserts need to be replaced, which can save time and money. In milling operations, several indexable inserts are positioned in a single milling cutter, which is then plunged, drilled, or moved around or across a workpiece that may be moving on multiple axes, depending on the milling machine. When the moving insert makes contact with the workpiece, it removes material. Each milling insert is designated by a series of letters and/or numbers that indicates several features of the insert such as geometry and size. Each insert also is made to a specific manufacturer grade, sometimes with a coating, that is suited for specific materials, applications, and operating conditions.
Milling inserts come in a large variety of shapes which are selected based on the specific indexable insert holder being used.
An important consideration when selecting indexable milling inserts is the cutter material, also known as the substrate. Various substrates bring specific characteristics to the tool; carbide, for example, and is resists abrasion and is harder than high-speed steel.
Also consider the finish or coating. To strengthen or add wear resistance to the substrate, many inserts have single or multilayer coatings applied through processes such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).
The pairing of the substrate and finish is referred to as the manufacturer grade. The grade determines how effectively the insert can machine specific materials in a range of operating conditions. It also determines the balance of shock and wear resistance the insert offers when machining specific materials in a range of operating conditions. Manufacturer grades are often proprietary compositions designated by the manufacturer.
Another consideration when selecting an insert is style. For milling inserts, the style is designated by a series of letters and numbers indicating whether the insert is left or right hand, the insert shape or type, the width, and the thickness. Insert styles vary for milling inserts depending on the type of tool, application, and operating conditions. The shape and size are chosen based on the specific indexable insert tool holder being used. Style designations are often specific to individual manufacturers.
Each insert has a chipbreaker geometry that allows the insert to break off and evacuate chips most efficiently in specific applications, such as roughing and finishing, and in operating conditions related to the machine and workpiece material. Milling insert chipbreaker geometries for specific operations and conditions are designated with two or more letters. For example, PL chipbreaker geometry is designed for light milling of steel.